Fixes #2641 - Add type_changed check to JS to allow form to refresh when provisioning a discovered host
Fixes #2642 - Display build button if host type has changed
Fixes #2643 - Check for operatingsystem before orchestrating TFTP
Fixes #2644 - Refactor Host find_by_name to use several ways to find a
host, and refactor my_hosts scope to Host::Base, allowing us to remove
unnecessary permissions check from find_by_name